Method and device for controlling semiconductor laser

ABSTRACT

The present invention relates to a semiconductor laser control method used preferably for a reading control system such as a bar code reading device and to a semiconductor laser control device employing the above method. The object of the invention is to provide a semiconductor laser control device which can be controlled based on the output of a semiconductor laser, provides a stable laser output in a noise environment, enables easy output adjustment, and is immune to external thermal or electrical noises. In the semiconductor laser control method where the light amount of a light amount to current controllable semiconductor laser is subjected to a feedback control with a predetermined time constant while it is monitored, when the light amount is less than a predetermined value, the semiconductor laser is subjected to an feedback control with a first time constant. When the light amount is more than a predetermined value, the semiconductor laser is subjected to a feedback control with a second time constant.

This application is a division of application Ser. No. 08/113,109, filedAug. 30, 1993, now U.S. Pat. No. 5,511,087.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor laser control methodand a semiconductor laser control device preferably used for a readingcontrol system such as a bar code reading device.

2. Description of the Related Art

In recent years, bar codes have been extensively utilized typically inPOS (point of sales) system in the distribution industry. Such acircumstance demands a small, low price, low power consumption bar codereading device. In order to answer such needs, semiconductor lasers havebeen used in place of conventional gas lasers.

FIG. 23 is a structural block diagram showing a bar code reading devicein which a semiconductor laser control device is used in the opticalsystem. In FIG. 23, numeral 1 represents a bar code printed on a surfaceof an article. The bar code 1 is formed of black bars and white barsarranged alternately and indicates specific datum based on the widthsthereof.

The optical system 2 irradiates a laser beam L2 to the bar-code andreceives the laser beam R1 reflected from the bar-code 1. The opticalsystem 2 also is formed of a semiconductor laser control device (laseremitter) 3, a scanning mechanism 4, and a photoelectric converter 5.

When the semiconductor laser control device 3 is activated under thecontrol of a CPU, it amplifies the laser output based on a predeterminedtime constant and holds automatically its light amount at apredetermined value.

As shown in FIG. 24, the semiconductor laser control device 3 isconstituted of a laser diode chip (LD chip) 30, a transistor 31, ananalog switch (SW) 34, operational amplifiers 36 and 38, a referencevoltage source 42, a capacitor 35, a variable resistor 37, and resistors32, 33, and 46. The LC chip 30 is formed of a laser diode (LD) 11 as asemiconductor laser, and a photo diode 12.

In such a circuit configuration, an external photo diode 12 detects acurrent Im showing a laser light amount. As shown in FIG. 25, theoperational amplifier 36 operates so as to equalize the voltage Va witha reference voltage Vref so that the LD drive current Iop from thesemiconductor laser is subjected to a feedback control to maintain thelaser light amount at a constant value.

In the operation, as shown by numerals (1) and (2) in FIGS. 25, when theanalog switch 34 is turned off (see time a) in response to a controlsignal from the CPU, the variable resistor 37 converts the monitoringcurrent Im as the detected laser light amount into a voltage Vacorresponding to a predetermined light amount.

The voltage VA (or VA1) is compared with the reference voltage Vref andis integrated by the operational amplifier 36 so that the output voltageVB of the operational amplifier 36, as shown in FIG. 25, rises, forexample, in accordance with a time constant of TcmV/sec from thereference voltage Vref. Then the output voltage VB of the amplifier 36is converted into an LD drive current Iop by the transistor 31.

When the voltage Va exceeds a threshold voltage after a period b oftime, or the LD drive current Iop exceeds a threshold current value ofthe laser diode 11, the laser diode 11 starts its laser oscillation.

Then the current Im from the external photo diode 12 increasesproportionally to the light amount while the voltage VA inputted to thenegative input of the operational amplifier 38 increases during a periodfrom the time b to the time c as shown in FIG. 25.

The output of the operational amplifier 36 is increased till the voltageVA is equalized with the reference voltage Vref. The operationalamplifier 36 equalizes the voltage VB with the reference voltage Vref soas to maintain the output voltage VB at a fixed value.

As a result, since the signal current sent to the base of the transistor31 is at a fixed value, the LD drive current Iop is maintained at afixed value, thus maintaining a laser output of the laser diode 11 at apredetermined value. The voltage changing rate depends on the referencevoltage Vref, the capacitor 35, and the resistor 46.

When the voltage reaches a predetermined value, the operationalamplifier 36 compensates variations in laser output variations due tovarious factors with the time constant so as to maintain thepredetermined value. When the analog switch 34 is turned on in responseto the control signal from the CPU, the operational amplifier 36provides the output at the reference voltage Vref so that the transistor31 is turned off to stop the laser oscillation.

The LD drive current lop of the laser diode 11 is increased inaccordance with the time constant because an abrupt LD drive current Iopproducing a predetermined light amount (after the time c in FIG. 25) maydestroy the laser diode 11.

FIG. 26 shows a modified semiconductor laser control device 3A. In thesemiconductor laser control device 3A, resistors 62 and 63 are connectedto the negative input of the forgoing semiconductor laser controldevice. A resistor 61 is added instead of the variable resistor 37 and avariable resistor 25 is inserted between the resistor 46 and theoperational amplifier 38.

The arrangement of the resistors 61, 62, and 63 converts the current Iminputted to the positive and negative inputs of the operationalamplifier 38 into a voltage with a predetermined ratio. The arrangementallows the variable resistor 25 to arrange to the output of theoperational amplifier 38 and to divide the voltage at the output of theoperational amplifier 38. Other configuration is similar to those in thesemiconductor laser control device 3.

In the semiconductor laser control devices 3 and 3A, the reason that thevariable resistors 37 and 25 are connected to the positive terminal ofthe operational amplifier 38 and the input of the resistor 46 will beexplained below.

As shown in FIG. 27, even if the laser diode 11 and the external diode12 used in the LD chip 30 are made of the same kind, the mountingcondition may cause variations several times in the monitoring currentIm of the laser diode 11 under the same light amount. For that reason, aproper negative input of the operational amplifier 36 may not beestablished with respect to light amount. However, the voltage divisiondue to the above layout of the variable resistor allows the voltage sentto the operational amplifier 36 to adjust at a proper value.

FIG. 27 shows the relationship between the voltage division ratio K andthe current Im at the optical amount P5 of 5 mW. The scale of thevoltage division ratio K is proportional to the angle of the resistancevarying knob of a variable resistor. As shown by the light amount overthe range between 2 mW to 4 mW in FIG. 27, the more the current Imincreases, the more the range between 2 mW and 4 mW narrows. There arethe relations of the current Im=(light amount P0)×(light amount P5)/5mW, the voltage Vm=(current Im)×(resistance value of the resistor 61),and K=(reference voltage Vref)+(voltage Vm), where light amount P0 is alight amount value varied with a voltage division ratio K with respectto a specific current Im.

In some cases, as shown in FIG. 28, a metal heat sink 28 is directly andelectrically contacted to the LD chip 30 to dissipate the heat generatedfrom it.

The scanning mechanism 4, shown in FIG. 23, is formed of a polygonmirror driven rotatably by, for example, a motor, and reflects the laserbeam L1 from the laser emitting unit 3. The laser beam L1 irradiates asa laser beam L2 to the bar code 1 including black bars and white barsand moves and scans at a fixed rate and perpendicularly to the bar code1.

The scanning mechanism 4 irradiates the reflected light R1 as thereflected light R2 to the photoelectric converting unit 5 while thereflected light R1 moves with the scanning of the laser beam L2.

Furthermore, the photoelectric converting unit 5 is formed of anphotoelectric element such as a photo diode, and converts the reflectedlight (optical input signal) R2 received via the scanning mechanism 4into an electric signal (analog value) corresponding to the lightamount.

Numeral 6 represents an aid converter for converting an electric signalfrom the photoelectric converting unit 5 to a digital signal. The aidconverter 6 also converts a binary signal including a black level signalcorresponding to the black bar portion of the bar code 1 and a whitelevel signal corresponding to the white bar portion thereof byconverting an electric signal from the photoelectric converting unit 5in a digital form. In the binary signal, since the light amount of thelight reflected from the white bar portion is larger than that from theblack bar portion, the white level signal is obtained as a high levelsignal and the black level signal is obtained as a low level signal.

Numeral 7 represents a bar width counter for counting the clock signalfrom the clock generator 8. The bar width counter 7 outputs the timewidths of the black level signal portion and the white level signalportion from the aid counter 6 or values corresponding to the black barwidth and the white bar width of an actual bar code 1, as a countedvalue of the clock signal.

Numeral 9 represents a memory for storing a bar counted value from thebar width counter 7 and 10 represents a CPU. The CPU 10 extracts anddemodulates specific data of the bar code 1 based on the bar widthcounted values (values corresponding to the each black bar width andeach white bar width) stored in the memory 9.

In the above structure, the laser beam L1 emitted from the laseremitting unit 3 is irradiated as the laser beam L2 to the black bar andthe white bar of the bar code 1 by the scanning mechanism 4, and ismoved and scanned at a fixed rate and perpendicularly to the black barand the white bar thereof.

The laser beam L2 from the scanning mechanism 4 is scattered andreflected by the bar code 1 and reentered as a light R1 reflected backto the scanning mechanism 4. The reflected light R1 moves at thescanning rate of the laser beam L2 while the reflection angle varies.When the reflected light R1 is reflected on the polygon mirror formingthe scanning mechanism 4, it enters onto the photoelectric element ofthe photoelectric converting unit 5 arranged at a predetermined place asthe reflection light R2.

The photoelectric converting unit 5 converts the reflected light R2 intoan electric signal corresponding to the light amount thereof. The a/dconverter 6 converts the electric signal to a signal in a digital formor a binary signal having a black level signal corresponding to a blackbar portion in a bar code 1 and a white level signal corresponding to awhite bar portion therein.

Then the bar width counter 7 counts the clock signals from the clockgenerator 8 and measures the time widths (values corresponding to thewidths of a black bar and a white bar of an actual bar code 1) of theblack level signal portion and the white level signal portion of abinary signal from the a/d converter 6, and stores the counted value ofthe clock signals temporarily into the memory 9. The CPU 10 subjects thebar width count value stored in the memory 9 to a specific demodulationprocess to extract and demodulate specific data from the bar code 1.

However, the semiconductor laser controller used for the above bar codereader cannot obtain the normal feedback current and voltage if noisedue to a factor is induced in the feedback system when the laser diodeemits properly a light beam of a predetermined light amount.

Thus the operational amplifier varies the output with a given timeconstant or the time constant ranging from an emitting time to the timeto a predetermined light amount even if the voltage is enough toestablish a predetermined light amount. However, there is a disadvantagein that since this time constant provides an excessive varying rate, thelaser diode emits abnormally before the feedback system in abnormalstate is detected.

Furthermore, there is a disadvantage in that the laser output is notstabilized at a predetermined light amount because the above timeconstant varies largely when the laser output is compensated to apredetermined light amount.

As shown in FIG. 27, when the current to a light amount is large, thescale in light amount is narrowed. Hence the voltage division ratio Kbetween 0.82 to 0.42 can be easily adjusted by a variable resistor.However, when the ratio is less than 0.42, the light amount adjustingbecomes difficult because the light amount varies coarsely at a slightvariation in angle of the knob of the variable resistor.

A heat sink mounted on a LD chip may conduct an undesired currentthrough the LD chip 30 because the heat sink in a shape provides anantenna effect to an electromagnetic wave and electrostatic electricity.As a result, there is a disadvantage in that the operational life of thelaser diode in the LD chip and an external photo diode becomes short.

SUMMARY OF THE INVENTION

The present invention is made to overcome the above mentioned problems.An object of the present invention is to provide a semiconductor lasercontrol device which can operate normally without being affected by anynoise in the feedback system for a period of time taking from anemitting start time till a time reaching a predetermined light amount,and which can produce a stable laser output at all times by compensatingproperly the laser output of a predetermined light amount varied due tovarious factors. The semiconductor laser control device also can adjusta variable resistor to a proper value and can prevent a laser diode andan external photo diode in an LD chip from external thermal orelectrical noises.

Another object of the present invention is to provide a method whichrealizes the above semiconductor laser control device.

In order to achieve the above objects, according to the presentinvention, a semiconductor control method wherein a light amount of alight amount to current controllable semiconductor laser is subjected toa feedback control based on a predetermined constant while saidsemiconductor laser is monitored, is characterized by the steps ofsubjecting the light amount of the semiconductor laser to a feedbackcontrol based on a first time constant when a light amount of thesemiconductor laser is less than a predetermined light amount; andsubjecting the light amount of the semiconductor laser a feedbackcontrol based on a second time constant when a light amount of thesemiconductor laser is more than the predetermined light amount.

A semiconductor laser control device according to the present inventionis characterized by a semiconductor laser permitting a light-amountcontrol in accordance with current; light amount monitoring means formonitoring a light amount of the semiconductor laser; first feedbackcontrol means for controlling a feedback of the light amount from thesemiconductor laser with a first time constant based on a monitoringresult from the light monitoring means; second feedback control meansfor controlling a feedback of the light amount of the semiconductorlaser with a second time constant based on a monitoring result from thelight amount monitoring means; and control mode selecting means forselecting a control mode by the first feedback control means when amonitoring result of the light amount monitoring means is less than apredetermined light amount and for selecting a control mode by thesecond control feedback means when the monitoring result is more thanthe predetermined light amount.

Furthermore, according to the present invention, a semiconductor lasercontrol method wherein a light amount to current controllablesemiconductor laser is subjected to a light amount feedback control witha predetermined time constant while the light amount is monitored, ischaracterized by the steps of controlling a feedback of a light amountof the semiconductor laser with a first time constant after apredetermined lapse of time when the semiconductor laser has beenchanged from an on state to an off state; and controlling a feedback ofa light amount of the semiconductor laser with a second time constantafter the predetermined lapse of time when the semiconductor laser hasbeen changed from an on state to an off state.

The predetermined time is set to be longer than a period of time whenthe semiconductor laser emits the predetermined light amount valuedefined by the first time constant.

A semiconductor laser control device according to the present inventionis characterized by a semiconductor laser permitting a light-amountcontrol in accordance with current; light amount monitoring means formonitoring a light amount of the semiconductor laser; first feedbackcontrol means for controlling a feedback of light amount from thesemiconductor laser with a first time constant based on a monitoringresult from the light amount monitoring means; second feedback controlmeans for controlling a feedback of the light amount of thesemiconductor laser with a second time constant based on a monitoringresult from the light amount monitoring means; on/off control means forcontrolling the on/off operation of the semiconductor laser; and controlmode selecting means for selecting a control mode of the first feedbackcontrol means after a predetermined period of time when thesemiconductor laser has been changed from an off state to an on state bysaid on/off control means, and for controlling a control mode of thesecond feedback control means after the predetermined period of timewhen the semiconductor laser has been changed from an off state to an onstate.

In this case, it is preferable that the predetermined time is set to belonger than a period of time till the light amount of the semiconductorlaser reaches a predetermined value based on the first time constant.

According to the present invention, a semiconductor laser control methodwherein a light amount of a light amount to current controllablesemiconductor laser is subjected to a feedback control based on apredetermined time constant while the semiconductor laser is monitored,is characterized by the steps of controlling a feedback of light amountof the semiconductor laser with a first time constant when a drivecurrent of the semiconductor laser is less than a predetermined drivecurrent; and controlling a feedback of light amount of the semiconductorlaser with a second time constant when a drive current of thesemiconductor laser is more than the predetermined drive current.

A semiconductor laser control device according to the present inventionis characterized by a semiconductor laser permitting a light-amountcontrol in accordance with current; light amount monitoring means formonitoring a light amount of the semiconductor laser; drive currentmeasuring means for measuring a drive current of the semiconductorlaser; first feedback control means for controlling a feedback of thelight amount of the semiconductor laser with a first time constant basedon a monitoring result from the light monitoring means; second feedbackcontrol means for controlling a feedback of the light amount of thesemiconductor laser with a second time constant based on a monitoringresult of the light amount monitoring means; and control mode selectingmeans for selecting a control mode of the first feedback control meanswhen a monitoring result from said drive current measuring means is lessthan a predetermined drive current, and for controlling a control modeof the second feedback control means when the monitoring result from thedrive current measuring means is more than the predetermined drivecurrent.

In this case, in the method and the device according to the presentinvention, it is preferable that the second time constant is set so asto be longer than the first time constant.

According to the present invention, a semiconductor laser control methodwherein a light amount of a light amount to current controllablesemiconductor laser is subjected to a feedback control based on apredetermined constant while the semiconductor laser is monitored, ischaracterized by the steps of controlling a feedback of said lightamount of said semiconductor laser based on a first time constant when adrive current of the semiconductor laser is less than a predeterminedvalue; controlling a feedback of light amount of the semiconductor laserbased on a second time constant when a drive current of thesemiconductor laser is more than the predetermined value; andcontrolling a feedback of the light amount of the semiconductor laserbased on a third time constant when a light amount of the semiconductorlaser is more than a predetermined light amount.

In this case, it is preferable that the third time constant is longerthan the second time constant, and the second time constant is longerthan the first time constant.

A semiconductor laser control device is characterized by a semiconductorlaser permitting a light-amount control in accordance with current;light amount monitoring means for monitoring a light amount of thesemiconductor laser; drive current measuring means for measuring a drivecurrent of the semiconductor laser; first feedback control means forcontrolling a feedback of the light amount of the semiconductor laserwith a first time constant based on a monitoring result from the lightmonitoring means; second feedback control means for controlling afeedback of light amount of the semiconductor laser with a second timeconstant based on a monitoring result from the light amount monitoringmeans; third feedback control means for controlling a feedback of thelight amount of the semiconductor laser with a third control timeconstant based on a monitoring result from the light amount monitoringmeans; and control mode selecting means for selecting a control mode ofthe first feedback control means when a drive current is less than apredetermined value based on a measuring result of the drive currentmeasuring means and the light amount monitoring means, for selecting acontrol mode of the second feedback control means when a drive currentis more than a predetermined value, and for selecting a control mode ofthe third feedback control means when a light amount is more than apredetermined value.

In this case, it is preferable that the third time constant is longerthan the second time constant, and the second time constant is longerthan the first time constant.

According to the present invention, a semiconductor laser control methodwherein a light amount of a light amount to current controllablesemiconductor laser is subjected to a feedback control based on apredetermined constant while the semiconductor laser is monitored, ischaracterized by the step of inputting a light amount monitoring signalto the feedback control means via a low pass filter when a light amountof the semiconductor laser is larger than a predetermined light amount.

Furthermore, a semiconductor laser control device according to thepresent invention is characterized by a semiconductor laser permitting alight-amount control in accordance with current; light amount monitoringmeans for monitoring a light amount of the semiconductor laser; feedbackcontrol means for controlling a feedback of the light amount of thesemiconductor laser with a predetermined light amount based on amonitoring result from the light amount monitoring means; low passfilter for passing a low frequency component of the monitoring resultfrom the light amount monitoring means; and selecting means forinputting the monitoring signal from the light amount monitoring meansto the feedback control means through the low pass filter when a lightamount is larger than a predetermined light amount based on themonitoring result from the light amount monitoring means.

According to the present invention, a semiconductor laser control methodwherein a light amount of a light amount to current controllablesemiconductor laser is subjected to a feedback control based on apredetermined constant while said semiconductor laser is monitored, ischaracterized by the step of inputting a light amount monitoring signalto the feedback control means via a low pass filter after apredetermined period of time when a light amount of the semiconductorlaser is larger than a predetermined light amount.

Moreover, a semiconductor laser control device according to the presentinvention is characterized by a semiconductor laser permitting alight-amount control in accordance with current; light amount monitoringmeans for monitoring a light amount of the semiconductor laser; feedbackcontrol means for controlling a feedback of the light amount of thesemiconductor laser with a predetermined light amount based on amonitoring result from the light amount monitoring means; low passfilter for passing a low frequency component of a monitoring result fromthe light amount monitoring means; and selecting means for inputting themonitoring signal from the light amount monitoring means to the feedbackcontrol means through the low pass filter after a predetermined periodof time when a light amount is larger than a predetermined light amountbased on the monitoring result from the light amount monitoring means.

According to the present invention, a semiconductor laser control methodwherein a light amount of a light amount to current controllablesemiconductor laser is subjected to a feedback control based on apredetermined constant while the semiconductor laser is monitored, ischaracterized by the step of inputting a light amount monitoring signalto the feedback control means via a low pass filter after apredetermined period of time when the semiconductor laser has beenchanged from an off state to an on state.

Furthermore, a semiconductor laser control device according to thepresent invention is characterized by a semiconductor laser permitting alight-amount control in accordance with current; light amount monitoringmeans for monitoring a light amount of the semiconductor laser; feedbackcontrol means for controlling a feedback of the light amount of thesemiconductor laser with a predetermined light amount based on amonitoring result from the light amount monitoring means; low passfilter for passing a low frequency component of a monitoring result fromthe light amount monitoring means; on/off control means for controllingthe on/off operation of the semiconductor laser; and selecting means forinputting a monitoring signal from the light amount monitoring means tothe feedback control means via the low pass filter after a predeterminedperiod of time when the semiconductor laser has been changed from an offstate to an on state by the on/off control means.

A semiconductor laser control device according to the present inventionis characterized by a semiconductor laser permitting a light-amountcontrol in accordance with current; light amount monitoring means formonitoring a light amount of the semiconductor laser as a current value;a current to voltage converter for converting a monitoring current fromthe light amount monitoring means into a voltage value; monitoringvoltage dividing means having two resistors serially connected to eachother to divide a monitoring voltage converted by the current to voltageconverter; feedback control means for controlling a feedback of thelight amount of the semiconductor laser so as to equalize the monitoringvoltage from said monitoring voltage dividing means to a referencevoltage; and a switch for short-circuiting one resistor in themonitoring voltage dividing means to change the voltage division ratio.

In this case, the monitoring voltage dividing means is constituted of avariable resistor, and a fixed value resistor serially connected to thevariable resistor and connected in parallel to the switch, and the fixedvalue resistor is set so as to have a resistance value at which thesemiconductor laser does not emit excessively when the variable resistoris set to a fixed resistance value even if the switch short-circuitselectrically the fixed resistor. It is preferable that the one resistoris formed of a variable resistor to vary continuously the voltagedivision ratio.

Furthermore, a heat dissipating member of a conductive material ismounted on said semiconductor laser for dissipating the semiconductorlaser through an intermediate member having a thickness equivalent tothat of a thermally contacted member. In this case, it is preferablethat heat dissipating member is grounded.

According to the first aspect of the present invention, thesemiconductor laser control device is constituted of a semiconductorlaser, light amount monitoring means, first feedback control means,second feedback control means, and control mode selecting means. Thesecond time constant is set to be longer than the first time constant.When the light amount of the semiconductor laser is less than apredetermined value, the light amount of the semiconductor laser issubjected to a feedback control in accordance with the first timeconstant. When the light amount of the semiconductor laser is more thana predetermined value, the light amount of the semiconductor laser issubjected to a feedback control in accordance with the second timeconstant. Therefore a predetermined light amount can be established at aproper glowing time. There is an advantage in that an error due tonoises in the feedback system can be compensated properly after thearrival at the light amount.

According to the second aspect of the present invention, thesemiconductor laser control device is constituted of a semiconductorlaser, light amount monitoring means, first feedback control means,second feedback control means, and control mode selecting means. Apredetermined time is set to be longer than the time when the lightamount of the semiconductor laser reaches at a predetermined value basedon the first time constant, and the second time constant is set to belonger than the first time constant. After the semiconductor laser haschanged from a non-glowing state to a glowing state, the light amount ofthe semiconductor laser is subjected to an feedback control based on thefirst time constant till a predetermined time. When the semiconductorlaser has changed from a non-glowing state to a glowing state, the lightamount of the semiconductor laser is subjected to a feedback controlbased on the second time constant after a lapse of the predeterminedtime. Hence the simplified structure can provide the similar advantageto that of the first aspect of the present invention.

According to the third aspect of the present invention, thesemiconductor laser control device is constituted of a semiconductorlaser, light amount monitoring means, drive current measuring means,first feedback control means, second feedback control means, and controlmode selecting means. The second time constant is set to be longer thanthe first time constant. When the drive current of the semiconductorlaser is less than a predetermined value, the light amount of thesemiconductor laser is subjected to a feedback control in accordancewith the first time constant. When the drive current of thesemiconductor laser is more than the predetermined value, the lightamount of the semiconductor laser is subjected to a feedback control inaccordance with the second time constant. Therefore the similaradvantage to that of the semiconductor laser control device according tothe first aspect of the invention can be obtained by arranging merely asmall device to the semiconductor laser control device. Thesemiconductor laser driving current can be increased effectively.

According to the fourth aspect of the present invention, thesemiconductor laser control device is constituted of a semiconductorlaser, light amount monitoring means, drive current measuring means,first feedback control means, second feedback control means, thirdfeedback control means, and control mode selecting means. The third timeconstant is set to be longer than the second time constant and thesecond time constant is set to be longer than the first time constant.When the drive current of the semiconductor laser is less than apredetermined value, the light amount of the semiconductor laser issubjected to a feedback control in accordance with the first timeconstant. When the drive current of the semiconductor laser is more thana predetermined value, the light amount of the semiconductor laser issubjected to a feedback control in accordance with the second timeconstant. When the light amount of the semiconductor laser is more thana predetermined value, the light amount of the semiconductor laser issubjected to a feedback control based on the third time constant.Therefore the similar advantages to those of the semiconductor lasercontrol device according to the first and third aspects of the inventioncan be obtained by arranging merely a small device to the semiconductorlaser control device. The semiconductor laser drive current can beincreased more effectively in comparison with the third aspect of thepresent invention.

According to the fifth aspect of the present invention, thesemiconductor laser control device is constituted of a semiconductorlaser, light amount monitoring means, feedback control means, a low passfilter, and control mode selecting means. When the light amount of thesemiconductor laser is more than a predetermined value, a light amountmonitoring signal is sent to the feedback control means via the low passfilter. There are advantages in that the similar effect to that of thesemiconductor laser control device of the first aspect of the presentinvention can be obtained and the choices in design can be widened.

According to the sixth aspect of the present invention, thesemiconductor laser control device is constituted of a semiconductorlaser, light amount monitoring means, feedback control means, a low passfilter, and control mode selecting means. After a predetermined periodof time when the light amount of the semiconductor laser control devicehas exceeded at a predetermined value, a light amount monitoring signalis inputted to the feedback control means via the low pass filter. Thusthe similar effect to that of the semiconductor laser control device ofthe fifth embodiment of the present invention can be obtained. Thetiming at which the light amount signal is passed through the low passfilter can be adjusted arbitrarily and effectively.

According to the seventh aspect of the present invention, thesemiconductor laser control device is constituted of a semiconductorlaser, light amount monitoring means, feedback control means, a low passfilter, on/off control means, and control mode selecting means. After apredetermined period of time when the semiconductor laser control devicehas changed from an off state to an on state, the light amountmonitoring signal is inputted to the feedback control means via the lowpass filter. Thus the similar effect to that of the semiconductor lasercontrol device in the sixth embodiment of the present invention can beeffectively obtained by a more simplified structure.

According to the eighth aspect of the present invention, thesemiconductor laser control device is constituted of a semiconductorlaser, light amount monitoring means, current/voltage converting means,monitoring voltage dividing means having two resistors, feedback controlmeans, and a switch for short-circuiting one of the resistors of themonitoring voltage dividing means to vary the voltage division ratio.Thus even if the monitoring current value is large, the light amount ofthe semiconductor laser can be adjusted sufficiently and effectively byusing the knob of a variable resistor.

Furthermore, the monitoring voltage dividing means is formed of avariable resistor and a fixed value resistor connected serially to eachother. A switch is connected in parallel to the resistor. Even if theswitch short-circuits the fixed resistor while the variable resistor isset to be a predetermined value, the laser output of the device can bestabilized because of the resistance value of the fixed resistor,whereby the overshooting can be prevented effectively.

Moreover there is an advantage in that one of the resistors is formed ofa variable resistor, the range of the voltage division ratio of thevariable resistor to the rotational angle of the knob can be adjustedarbitrarily and continuously.

According to the ninth aspect of the present invention, a heatdissipating member of conductive material is mounted on a semiconductorlaser via an intermediate member of non-conductive material having athickness equivalent to that of the thermally contacted member. Hencesince the heat generated in the semiconductor laser and the light amountmonitoring means in the semiconductor laser control device can bereleased, the semiconductor laser and the light amount monitoring meanscan be prolonged in its operational life. Moreover, the heat dissipatingmember grounded can prevent an undesired current from flowing thesemiconductor laser and the light amount monitoring means so that eachelement can be effectively prolonged in its operational life.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a principle block diagram showing the first aspect of thepresent invention;

FIG. 2 is a principle block diagram showing the second aspect of thepresent invention;

FIG. 3 is a principle block diagram showing the third aspect of thepresent invention;

FIG. 4 is a principle block diagram showing the fourth aspect of thepresent invention;

FIG. 5 is a block diagram showing the fifth and sixth aspects of thepresent invention;

FIG. 6 is a principle block diagram showing the seventh aspects of thepresent invention;

FIG. 7 is a principle block diagram showing the eighth aspect of thepresent invention;

FIG. 8 is a principle block diagram showing the ninth aspect of thepresent invention;

FIG. 9 is a circuit diagram showing the first embodiment of the presentinvention;

FIG. 10 is a block diagram showing the functions of the first and thesecond embodiments of the present invention;

FIG. 11 is a circuit block diagram showing the second embodiment of thepresent invention;

FIG. 12 is a circuit block diagram showing the third embodiment of thepresent invention;

FIG. 13 is a block diagram showing the function of the third embodimentof the present invention;

FIG. 14 is a circuit block diagram showing the fourth embodiment of thepresent invention;

FIG. 15 is a block diagram showing the function of the fourth embodimentof the present invention;

FIG. 16 is a circuit block diagram showing the fifth embodiment of thepresent invention;

FIG. 17 is a circuit block diagram showing the sixth embodiment of thepresent invention;

FIG. 18 is a circuit block diagram showing the seventh embodiment of thepresent invention;

FIG. 19 is a circuit block diagram showing the eighth embodiment of thepresent invention;

FIG. 20 is a diagram explaining the function of the eighth embodiment ofthe present invention;

FIG. 21 is a cross sectional view showing a heat sink mounted on a laserdiode chip;

FIG. 22 is a diagram showing a heat sink mounted on a laser diode chip;

FIG. 23 is a circuit block diagram showing a bar code reading device;

FIG. 24 is a circuit block diagram showing a semiconductor laser controldevice;

FIG. 25 is a block diagram showing the function of the semiconductorlaser control device;

FIG. 26 is a circuit block diagram showing another semiconductor lasercontrol device;

FIG. 27 is a block diagram showing the voltage division ratio vs currentcharacteristic of a semiconductor laser control device; and

FIG. 28 is a model diagram showing a heat sink mounted on a laser diodechip in a semiconductor laser control device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the attached drawings, an explanation will be made indetail as for preferred embodiments of the method and device forcontrolling a semiconductor laser according to the present invention.

(a) Explanation of the Principle of the Invention

FIG. 1 is a block diagram showing the first aspect of the presentinvention. In FIG. 1, a semiconductor laser control device 20A isconstituted of a semiconductor laser 11, light amount monitoring means12, first feedback control means 13, second feedback control means 14,control mode selecting means 15A, and a power source 29.

The semiconductor laser 11 is a light amount controllable lasercontrolled with current. The light amount monitoring means 12 monitorsthe light amount of the semiconductor laser 11.

The first feedback control means 13 executes a feedback control of thelight amount of the semiconductor laser 11 with the first time constantbased on the monitoring result from the light amount monitoring means12. The second feedback control means 14 executes a feedback control ofthe light amount of the second semiconductor laser 11 with a second timeconstant based on the monitoring result from the light amount monitoringmeans 12.

The control mode selecting means 15A selects a control mode selected bythe first feedback control means 13 based on the monitoring result fromthe light amount monitoring means 12 when the light amount is less thana predetermined value, and selects a control mode selected by the secondfeedback control means 14 when the light amount is more than thepredetermined value. The second time constant is set to be longer thanthe first time constant.

FIG. 2 is a principle diagram showing the second aspect of the presentinvention. In FIG. 2, numeral 20B represents a semiconductor lasercontrol device. The semiconductor laser beam device 20B is constitutedof a semiconductor laser 11, a light amount monitoring means 12, firstfeedback control means 13, second feedback control means 14, controlmode selecting means 15B, on/off control means, and a power source 29.

As for the semiconductor laser 11, the light amount monitoring means 12,the first feedback control means 13, and the second feedback controlmeans 14, the explanation has been made with reference to the firstaspect of the invention. In the first feedback control means 13 and thesecond feedback control means 14, the first time constant is set to belonger than the second time constant, in the similar manner to thesemiconductor laser control device 20A.

The control mode selecting means 15B selects a control mode selected bythe first feedback control means 13 for a predetermined period of timewhen the on/off control means 16 has changed the semiconductor laser 11from an on state to an off state, and selects a control mode selected bythe second feedback control means 14 after the predetermined period oftime when the on/off control means 16 has changed the semiconductorlaser 11 from an off state to an on state.

The predetermined time is set to be longer than the time that thesemiconductor laser 11 emits a light beam of a predetermined lightamount in accordance with the first time constant of the first feedbackcontrol means 13. The first time constant is set to be longer than thesecond time constant.

FIG. 3 is a principle block diagram showing the third aspect of thepresent invention. In FIG. 3, the semiconductor laser control device 20cis consisted of a semiconductor laser 11, light amount monitoring means12, a first feedback control means 13, second feedback control means 14,control mode selecting means 15C, drive current measuring means 17, anda power source 29.

As for the semiconductor laser 11, the light amount monitoring means 12,the first feedback control means 13, the second feedback control means14, the functions are similar to those explained with the first aspectof the invention. In the first feedback control means 13 and the secondfeedback means 14, the first time constant is set to be longer than thesecond time constant, as described with the semiconductor laser controldevice 20A.

The drive current measuring means 17 measures the drive current of thesemiconductor laser 11. The control mode selecting means 15C selects acontrol mode by means of the first feedback control means 13 based onthe measuring result from the drive current measuring means 17 when thedrive current is less than a predetermined value. When the drive currentis more than the predetermined value, the control mode selecting means15C selects a control mode by means of the second feedback control means14.

FIG. 4 is a principle block diagram showing the fourth aspect of thepresent invention. In FIG. 4, numeral 20D represents a semiconductorlaser control device. The semiconductor laser control device 20D isconstituted of a semiconductor laser 11, light amount monitoring means12, first feedback control means 13, second feedback control means 14,third feedback control means 18, control mode selecting means 15D, drivecurrent measuring means 17, and a power source 29.

As for the semiconductor laser 11, the light amount monitoring means 12,the first feedback control means 13, the second feedback control means14, and the drive current measuring means 17, the functions are similarto those explained with the third aspect of the invention. The thirdfeedback control means 18 perform a feedback control of the light amountfrom the semiconductor laser 11 with the third time constant, based onthe monitoring result from the light amount monitoring means 12.

The control mode selecting means 15D selects a control mode by means ofthe first feedback control means 13 based on the measuring result of thedrive current measuring means 17 and the light amount monitoring means12 when the drive current is less than a predetermined value. Thecontrol mode selecting means 15D also selects a control mode by means ofthe second feedback control means 14 when the drive current is more thana predetermined value and selects a control mode by means of the thirdfeedback control means 18 when the light amount is more than apredetermined value.

The third time constant is set to be longer than the second timeconstant and the second time constant is set to be longer than the firsttime constant.

FIG. 5 is a principle block diagram showing the fifth aspect of theinvention. In FIG. 5, numeral 20E represents a semiconductor lasercontrol device. The semiconductor laser control device 20E is formed ofa semiconductor laser 11, light amount monitoring means 12, selectingmeans 15E, a low pass filter 19, and feedback control means 21.

As for the semiconductor laser 11 and the light amount monitoring means12, the functions are similar to those described in the first aspect ofthe invention. The feedback control means 21 executes a feedback controlof the light amount of the semiconductor laser 11 with a predeterminedtime constant based on the monitoring result of the light amountmonitoring means 12. The low pass filter 19 passes the low frequencycomponent of the monitoring signal from the light amount monitoringmeans 12.

The selecting means 15E inputs the monitoring signal from the lightamount monitoring means 12 to the feedback control means 21 via the lowpass filter 19 based on the monitoring result from the light amountmonitoring means 12 when the light amount is more than a predeterminedvalue.

FIG. 5 is a principle diagram showing the sixth aspect of the presentinvention. In FIG. 5, numeral 20F represents a semiconductor lasercontrol device. The semiconductor laser device 20F is formed of asemiconductor laser 11, light amount monitoring means 12, selectingmeans 15F, a low pass filter 19, a power source 29, and feedback controlmeans 21.

As for the semiconductor laser 11, the light amount monitoring means 12,the low pass filter 19, and the feedback control means 21, the functionsare similar those described with the first and fifth aspects of thepresent invention. The selection means 15F inputs the monitoring signalfrom the light amount monitoring means 12 to the feedback control means21 via the low pass filter based on the monitoring result of the lightamount monitoring result 12 after a predetermined period of time whenthe light amount has been more than the predetermined value.

FIG. 6 is a principle diagram showing the seventh aspect of theinvention. In FIG. 6, numeral 20G represents a semiconductor lasercontrol device. The semiconductor laser control device 20G isconstituted of a semiconductor laser 11, light amount monitoring means12, selecting means 15G, on/off control means 16, a low pass filter 19,a power source 29, and feedback control means 21. The semiconductorlaser 11, the light amount monitoring means 12, the on/off control means16, the low pass filter 19, and the feedback control means 21 have beenexplained with the first and fifth aspects of the present invention.

The selecting means 15G inputs the monitoring signal from the lightamount monitoring means 12 to the feedback control means 21 via the lowpass filter after a predetermined period of time when the on/off controlmeans 16 has changed the semiconductor laser 11 from an off state to anon state.

FIG. 7 is a principle diagram showing the eighth aspect of the presentinvention. In FIG. 7, numeral 20 is a semiconductor laser controldevice. The semiconductor laser control device 20 is constituted of asemiconductor laser 11, light amount monitoring means 12,current/voltage converting means 22, and monitoring means 23, and apower source 29.

The semiconductor laser 11 and the light amount monitoring means 12 actas described in the foregoing aspects of the present invention. Thecurrent/voltage converting means 22 converts the monitoring current fromthe light amount monitoring means 12 into a voltage. The monitoringvoltage dividing means 23 divides a monitoring voltage converted by thecurrent/voltage converting means 22, and is formed of two resistors 25and 26 connected serially to each other.

The switch 24 is arranged across the resistor 26 in the monitoringvoltage dividing means 23 and short-circuits electrically the resistor26 to vary the voltage division ratio. The feedback control means 15Hexecutes a feedback control of the light amount of the semiconductorlaser 11 so as to equalize the monitoring dividing signal from themonitoring voltage dividing means 23 with a reference voltage. Theresistor 26 may be a variable resistor to vary continuously the voltagedividing ratio.

The monitoring voltage dividing means 23 may be formed of a variableresistor 25, a fixed resistor 26 serially connected to each other, and aswitch 24 connected in parallel with the fixed resistor 26. In thiscase, when the variable resistor 25 is set to a predetermined position,the fixed resistor 26 has a resistance value that a semiconductor laser11 does not emit excessively even if the switch 24 short-circuitselectrically the fixed resistor 26 when the variable resistor 25 is setto a predetermined position.

FIGS. 8 is principle diagrams showing the ninth aspect of the presentinvention. In FIG. 8, numeral 11 represents a light emitting diode. Thelight emitting diode 11 is mounted on the heat dissipating member 28 ofa conductive material via an intermediate member 27 of non-conductivematerial. The intermediate member 27 is made of a non-conductivematerial having a thickness equivalent to that contacted thermally. Theheat dissipating member 28 is formed of a heat conductive material todissipate the heat from the semiconductor laser 11. The heat dissipatingmember 28 is grounded.

According to the first aspect of the invention, as shown in FIG. 1, thesemiconductor laser control device 20A executes a feedback of the lightamount of the semiconductor laser 11 with a predetermined time constantwhile a light amount is monitored by the light amount monitoring means12 of the semiconductor laser 11. As a result, the light amount controlis performed by adjusting the current to the semiconductor laser 11.

The selection of the time constant in the light amount control isperformed by the control mode selecting means 15A. That is, when thelight amount from the semiconductor laser 11 is less than apredetermined value, the first feedback control means 13 selects acontrol mode to perform a feedback control of the semiconductor laser 11with the second time constant longer than the first time constant byselecting a control mode by the second feedback control means when thelight amount exceeds a predetermined value.

In the second aspect of the present invention, as shown in FIG. 2, thesemiconductor laser control device 20B performs a feedback control ofthe semiconductor laser 11 with a predetermined time constant while thelight amount monitoring means 12 to the semiconductor laser 11 monitorsthe light amount.

The selection of the time constant in the feedback control is performedby the control mode selection means 15B. When the on/off control means16 controls the semiconductor laser 11 from an on state to an off state,the first feedback control means 13 selects the control mode for apredetermined time, thus performing a feedback control of thesemiconductor laser 11 with the first time constant longer than thesecond time constant. As a result, the light amount of the semiconductorlaser 11 reaches to a predetermined value in the predetermined period oftime with the first time constant.

On the other hand, when the semiconductor laser 11 changes from an offstate to an on state, the second feedback control means 14 selects thecontrol mode after a lapse of the predetermined time and the lightamount of the semiconductor laser 11 is subjected to an feedback controlin accordance with the second time constant.

In the third aspect of the present invention, as shown in FIG. 3, thesemiconductor laser control device 20C performs a feedback control ofthe semiconductor laser 11 with a predetermined time constant while thelight amount monitoring means 12 to the semiconductor laser 11 ismonitored.

The selection of the time constant in the feedback control is performedby the control mode selection means 15C. Namely, the drive currentmeasuring means 17 measures the drive current of the semiconductor laser11. When the drive current of the semiconductor laser 11 is less than apredetermined value, the first feedback control means 13 selects thecontrol mode, so that the light amount of the semiconductor laser 11 issubjected to a feedback control with the first time constant.

On the other hand, when the drive current of the semiconductor laser 11is larger than the predetermined value, the second feedback controlmeans 14 selects the control mode, so that the light amount of thesemiconductor laser 11 is subjected to an feedback control in accordancewith the second time constant.

According to the fourth aspect of the present invention, as shown inFIG. 4, the semiconductor laser control device 20D executes a feedbackof the light amount of the semiconductor laser 11 in accordance with thepredetermined time constant while the light amount monitoring means 12for the semiconductor laser 11 monitors the light amount.

The selection of the time constant in the feedback control is performedby the control mode selecting means 15D and based on the measuringresult of the drive current measuring means 17 and the light amountmonitoring means 12.

When the drive current of the semiconductor laser 11 is less than apredetermined value, the first feedback control means 13D selects thecontrol mode, so that the light amount of the semiconductor laser 11 issubjected to a feedback control in accordance with the first timeconstant.

When the drive current of the semiconductor laser 11 is larger than apredetermined value, the second feedback control means 14D selects thecontrol mode, so that the light amount of the semiconductor laser 11 issubjected to a feedback control in accordance with the second timeconstant longer than the first time constant.

When the light amount of the semiconductor laser 11 is larger than thepredetermined value, the third feedback control means 18 selects thecontrol mode, so that the light amount of the semiconductor laser 11 issubjected to a feedback control in accordance with the third timeconstant longer than the second time constant.

In the fifth aspect of the present invention, as shown in FIG. 5, thesemiconductor laser control means 20E executes a feedback of the lightamount of the semiconductor laser 11 in accordance with a predeterminedtime constant while the light amount monitoring means 12 for thesemiconductor laser 11 monitors the light amount.

That is, when the light amount of the semiconductor laser 11 is lessthan a predetermined value, the feedback control means 21E subjects thelight amount of the semiconductor laser 11 to a feedback control inaccordance with the predetermined time constant based on the monitoringresult from the light amount monitoring means 12.

The selecting means 15E inputs the light amount monitoring signal to thefeedback control means 21E via the low pass filter 19 based on themonitoring result from the light amount monitoring means 12 when thelight amount of the semiconductor laser 11 becomes larger than thepredetermined value. In this case, the low pass filter 19 passes the lowfrequency component of the monitoring signal.

In the sixth aspect of the present invention, as shown in FIG. 5, thesemiconductor laser control device 20F controls the feedback of thelight amount of the semiconductor laser 11 in accordance with apredetermined time constant while the light amount monitoring means 12of the semiconductor laser 11 monitors the light amount.

The light amount of the semiconductor laser 11 is subjected to afeedback control by the feedback control means 21F with thepredetermined time constant based on the monitoring result from thelight amount monitoring means 12 for a predetermined period of timeafter the light amount of the semiconductor laser 11 has exceeded thepredetermined value .

For the predetermined period of time after the light amount from thesemiconductor laser 11 has exceeded the predetermined value, theselecting means 15F passes the light amount monitoring signal to thefeedback control means 21F via the low pass filter 19. In this case, thelow pass filter 19 passes the low frequency component of the monitoringsignal.

In the seventh aspect of the present invention, as shown in FIG. 6, thesemiconductor laser control device 20F executes a feedback control ofthe light amount from the semiconductor laser 11 with a predeterminedtime constant while the light amount monitoring means 12 for thesemiconductor laser 11 monitors the light amount.

After a lapse of a predetermined time when the semiconductor laser 11has changed from an off sate to an on state, the selecting means 15Ginputs the light amount monitoring signal to the feedback control means21G through the low pass filter 19. In this case, the low pass filter 19passes the low frequency component of the monitoring signal.

In the eighth aspect of the present invention, as shown in FIG. 7, thecurrent, which indicates the light amount from the semiconductor laser11 detected by the light amount monitoring means 12 in the semiconductorlaser control device 20, is converted into a voltage by means of thecurrent/voltage converting means 22 and the voltage is divided by themonitoring voltage dividing means 23.

The feedback control means 15H executes a feedback control of the lightamount of the semiconductor laser 11 so as to equalize the monitoringdivided voltage signal form the monitoring voltage dividing means 23with the reference voltage. When the voltage division ratio is varied,the switch 24 connected across the resistor 26 in the monitoring voltagedividing means 23 short-circuits electrically the resistor 26.

The monitoring voltage dividing means 23 is formed of a variableresistor 25 and a fixed resistor 26 serially connected to each other.When the switch 24 is connected in parallel to the fixed resistor 26 setto a predetermined position, the semiconductor laser 11 does not emitexcessively even if the switch short-circuits the resistor 26 when thevariable resistor 25 is set to a predetermined position. If the resistor26 is a variable resistor, the voltage division ratio is variedcontinuously and purposely.

The semiconductor laser control device in the ninth aspect of thepresent invention, as shown in FIG. 8, the heat generated in thesemiconductor laser 11 is conducted to the heat dissipating member 28via the intermediate member 27 to dissipate externally.

Even if noises due to external electromagnetic waves or electrostaticelectricity are transmitted to the semiconductor laser 11 through theheat dissipating member 28, the electricity charged on the heat sinkmember 28 is released because of the shielding effect of theintermediate member 27 and the heat dissipating member 28 grounded.

According to the first aspect of the invention, since the structure isformed of the semiconductor laser 11, the light amount monitoring means12, the first feedback control means 13, the second feedback controlmeans 14, and the control mode selecting means 15A. The second timeconstant is set to be longer than the first time constant. When thelight amount of the semiconductor laser is less than a predeterminedvalue, the light amount of the semiconductor laser is subjected to afeedback control in accordance with the first time constant. When thelight amount is set to be more than the predetermined value, the lightamount of the semiconductor laser is subjected to a feedback control inaccordance with the second time constant. Therefore there is anadvantage in that a predetermined light amount can be obtained in asuitable emitting time and a proper compensation can be made to errorsdue to noise in the feedback system after a predetermined light amounthas been established.

According to the second aspect of the present invention, the structureincludes a semiconductor laser 11, light amount monitoring means 12,first feedback control means 13, second feedback control means 14, and acontrol mode selecting means 15B. The predetermined time is set to belonger than time that the semiconductor laser settles to thepredetermined light amount in accordance with the first time constant.The second time constant is set to be longer than the first timeconstant. The light amount of the semiconductor laser is subjected to afeedback control with the first time constant after a predeterminedperiod of time when the semiconductor laser has changed from an offstate to an on state. The light amount of the semiconductor laser issubjected to a feedback control with the second time constant for apredetermined period of time when the semiconductor laser has changedfrom an off state to an on state. The similar advantage to that of thefirst aspect of the present invention can be obtained by the simplifiedstructure.

According to the third aspect of the present invention, the structureincludes a semiconductor laser 11, light amount monitoring means 12,drive current measuring means 17, first feedback control means 13,second feedback control means 14, and control mode selecting means 15C.The second time constant is set to be longer than the first timeconstant. The light amount of the semiconductor laser is subjected to afeedback control with the first time constant when the drive current ofthe semiconductor laser is less than a predetermined value. The lightamount of the semiconductor laser is subjected to a feedback controlwith the second time constant when the drive current of thesemiconductor laser is more than the predetermined value. The similaradvantage to that of the semiconductor laser control device according tothe first aspect of the present invention can be realized by addingmerely a small device to the semiconductor laser control device by thesimplified structure. The semiconductor laser drive current can beincreased effectively.

According to the fourth aspect of the present invention, the structureincludes a semiconductor laser 11, light amount monitoring means 12,drive current measuring means 17, first feedback control means 13,second feedback control means 14, third feedback control means 18, andcontrol mode selecting means 15D. The third time constant is set to belonger than the second time constant. The second time constant is set tobe longer than the first time constant. The light amount of thesemiconductor laser is subjected to a feedback control with the firsttime constant when the drive current of the semiconductor laser is lessthan the predetermined value. The light amount of the semiconductorlaser is subjected to a feedback control with the second time constantwhen the drive current of the semiconductor laser is more thanpredetermined value. The light amount of the semiconductor laser issubjected to a feedback control with the third time constant when thelight amount of the semiconductor laser is more than a predeterminedvalue. The similar advantages to those of the semiconductor lasercontrol devices according to the first and third aspects of the presentinvention can be obtained by adding merely a small device to thesemiconductor laser control device. The semiconductor laser drivecurrent can be increased effectively more than the third aspect of theinvention.

According to the fifth aspect of the present invention, the structureincludes a semiconductor laser 11, light amount monitoring means 12,feedback control means 21, a low pass filter 19, and selecting means15E. When the light amount of the semiconductor laser is more than thepredetermined value, the light amount monitoring signal is inputted tothe feedback control means via the low pass filter. Thus there is anadvantage in that the degree of freedom in design is widened while thesimilar advantage to that of the semiconductor laser control devicesaccording to the first aspect of the present invention.

According to the sixth aspect of the present invention, the structureincludes a semiconductor laser 11, light amount monitoring means 12,feedback control means 21, a low pass filter 19, and selecting means15F. The light amount of the semiconductor laser is inputted to thefeedback control means via the low pass filter after a predeterminedperiod of time when the drive current of the semiconductor laser is morethan the predetermined value. The similar advantages to that of thesemiconductor laser control devices according to the fifth aspect of thepresent invention can be obtained. Moreover the timing to pass the lightamount monitoring signal to the low pass filter can be freely adjustedeffectively.

According to the seventh aspect of the present invention, the structureincludes a semiconductor laser 11, light amount monitoring means 12,feedback control means 21, a low pass filter 19, on/off control means16, and selecting means 15G. The light amount monitoring signal isinputted to the feedback control means via the low pass filter after apredetermined period of time when the semiconductor laser is changedfrom an off state to an on state. The similar advantages to that of thesemiconductor laser control devices according to the sixth aspect of thepresent invention can be obtained effectively by a simplified structure.

According to the eighth aspect of the present invention, the structureincludes a semiconductor laser 11, light amount monitoring means 12,current/voltage converting mans 22, monitoring voltage dividing means 23having two resistors, and feedback control means 15H. The structure alsoincludes a switch 24 for short-circuiting one resistor 26 in themonitoring voltage dividing means 23 to vary the voltage division ratio.Hence there is an advantage in that even if the monitoring current valueis large, a variable resistor can adjust sufficiently the light amountof the semiconductor laser by using the knob thereof.

Furthermore, the monitoring voltage dividing means 23 is formed by avariable resistor 25 and a fixed value resistor 26 connected serially toeach other. A switch 24 is connected across the fixed value resistor 26.When the variable resistor 25 is set to a predetermined position and thefixed value resistor 26 is short-circuited, the fixed resistor 26 is setto a resistance value not to emit excessively the semiconductor laser sothat the device can produce effectively its output stabilized and withno overshoot.

Since one resistor is formed as a variable resistor 25 which variescontinuously the voltage division ratio, the range of the voltagedivision ratio of the resistance to the rotation angle of the knob ofthe variable resistor 25 can be adjusted freely.

According to the ninth aspect of the present invention, the heat sinkmember 28 of a conductive material is mounted on the semiconductor laser11 through an intermediate member 27 of non-conductive material having athickness thermally equivalent to the contacted member dissipating theheat from the semiconductor laser 11. Thus there is an advantage in thatthe heat from the semiconductor laser of the semiconductor laser controldevice and the light amount monitoring means can be released externallyso that the operational life span thereof can be prolonged.

There is an advantage in that the heat dissipating member 28 groundedcan prevent an undesired current flowing through the semiconductor laserand the light amount monitoring means, whereby a prolonged operationallife of each device can be obtained.

(b) Explanation of the First Embodiment

The embodiments according to the present invention will be explainedbelow with reference to attached drawings.

FIG. 9 is a block diagram showing the first embodiment of the presentinvention. In FIG. 9, numeral 20A represents a semiconductor lasercontrol device. The semiconductor laser control device 20A is arrangedin place to the semiconductor laser control devices 3 and 3A. Thesemiconductor laser control device 20A is constituted of an LD chip(laser diode chip) 30 including a laser diode 11 and a photo diode(light amount monitoring means) 12, a transistor 31, analog switches(SW) 34 and 39, amplifiers (operational amplifiers) 36 and 38,comparator (control mode selecting means) 45, a reference voltage source42, a capacitor 35, a variable resistor 37, and resistors 32, 33, 40,41, 43, and 44. Like numerals represent like elements in the relatedart.

The laser diode 11 emits bidirectionally the laser beam when the LDdrive current Iop over a predetermined value flows. An external photodiode 12 receives one of the two laser beams with the light receivingsurface and outputs the monitoring current Im corresponding to the lightamount. The current Im from the photo diode 12 is outputted through thevariable resistor 37 and the amplifier 38. FIG. 10 shows therelationship between the voltage VA after the time b and theproportional constant K (VA=KIm, where VA is a voltage after the timeb).

The external photo diode 12 outputs the current Im proportional to thevoltage Vcc when the voltage Vcc is applied forwards without receiving alight on the light receiving surface. The current Im from the photodiode 12 is outputted through the variable resistor 37 and the amplifier38. In FIG. 10, the current is proportional to the voltage VA betweenthe time a and the time b in accordance with the proportional constant m(VA=mIm where VA is a voltage between the time a and the time b, K>m).

As described in the prior art, the variable resistor 37 converts thecurrent Im to a voltage and adjusts the relation between the current Imand the light amount through the voltage division. The operationalamplifier 38 compares the voltage from the variable resistor 37 with theself output. If the voltage from the variable resistor 37 is higher thanthe feedback voltage, it is outputted to the output side thereof.

The operational amplifier 36 compares the voltage VA from the amplifier38 through the resistor with the reference voltage Vref from thereference voltage source 42, and maintains the voltage VB as it is ifboth values are equalized.

The capacitor 35 is connected across the amplifier 36 so as to couplethe voltage VA of the negative input side to the voltage of the outputside. The resistors 40 and 41 are connected in parallel between theamplifiers 36 and 38. If the compared result between the voltage VA andthe reference voltage Vref is different, a process is performed asfollows: if the output voltage VA<the reference voltage Vref, thevoltage VB is increased with a predetermined time constant, or if theoutput voltage VA>the reference voltage Vref, the voltage VB isdecreased from the reference voltage Vref with the predetermined timeconstant. The operational amplifier 36 operates so as to equalize thevoltage VA with the reference voltage Vref to maintain the output at afixed value in the feedback system. The reference voltage Vref appliedon the positive input side of the operational amplifier 36 is integratedin accordance with a predetermined time constant.

The time constant determining the degree of the variation in the outputvoltage VB is determined by the dimensions of the capacitor 35, theresistors 40 and 41, and the reference voltage Vref. The time constantis changed by the on/off operation of the analog switch 39 connectedserially to the resistor 40. That is, when the analog switch 39 is in anoff state, the output voltage VB of the operational amplifier 36 isintegrated with a first time constant of, for example, Tc/100 mV/sec(μA/μsec). When the analog switch 39 is in an on state, the outputvoltage VB of the operational amplifier 36 is integrated with a secondtime constant of, for example, TcmV/sec (100 μA/μsec). The second timeconstant is set to be longer than the first time constant. The timeconstant depends on a period of time which reaches a predetermined valuein accordance with the time constant. A small constant has a long timeconstant. As understood from the time constant, the resistance ratio ofthe resistors 40 and 41 is expressed as resistor 40/resistor 41=100/1.

In the present circuit, the resistor 40 is selected under the control ofthe analog switch 39 to add it as the time constant determining factor.Thus two feedback control devices with different time constants arearranged. When one of the control devices is selected, a feedbackcontrol of the light amount of the laser diode 11 is performed with thetime constant.

The analog switch 34 is turned on in accordance with the control of theCPU to short-circuit the amplifier 36. The analog switch 39, asdescribed above, is arranged so as to connect or disconnect the resistor40, and is controlled based on the output (see (3) in FIG. 10) from thecomparator 45. The transistor 31 has a collector connected forwards tothe output of the laser diode 11, a base connected to the resistor 32and the branched resistor 33 for receiving as the current signal IB viathe resistor 32 the signal voltage VB to control the light emittedamount from the laser diode 11, and an emitter grounded. The resistor 33is grounded. The transistor 31 controls the correct signal current Iopfrom the laser diode 11 to the amount proportional to the base signalcurrent IB.

The comparator 45 compares the voltage VA from the amplifier 38corresponding to the light amount of the laser diode 11 with the voltageof 90% of the reference voltage Vref from the reference voltage source42. If the voltage V<90% of the reference voltage Vref, the outputbecomes an H level and if the voltage VA>90% of the reference voltageVref, the output becomes an L level.

The comparator 45 can select automatically the time constant fordetermining an increasing and decreasing rate of the output voltage VBfrom the operational amplifier 36, based on a monitoring result from theexternal photo diode 12. That is, when the monitoring result of theexternal photo diode 12 is less than the predetermined value (referencevoltage Vref×0.9), the control mode of the time constant Tc mV/sec) isselected if the resistor 40 is connected. When the monitoring result islarger than the predetermined light amount q and the resistor 40 isdisconnected, the control mode of the time constant Tc/100 mV/sec isselected.

The receiving portion of the comparator 45 is connected between theresistors 43 and 44 to receive 90% of the reference voltage Vref. Oneterminal of the resistor 44 is connected to the output side of thereference power source 42. The resistor 44 is grounded in the similarmanner to that to the resistor 33. That is, the resistors 43 and 44 arearranged to make 90% of the reference voltage Vref from the referencevoltage source 42.

According to the above structure, the external photo diode 12 detectsthe current Im indicating the light amount of the laser, and the LDdrive current Iop is controlled based on the current Im to maintain thelight amount of the laser at a fixed value.

A detail explanation will be made below as for the operations for theperiod between time a and time b, the period between time b and time c,and the period after the time c, as shown in FIG. 10.

Referring to FIG. 10, the operation between the time a and the time b ofthe semiconductor laser control device 20A is explained. As shown with(1) and (2) in FIG. 10, when the analog switch 34 is turned off inresponse to the control signal from the CPU, the current Im indicating adetected laser light amount is converted to a voltage VA by means of thevariable resistor 37. In this case the current Im has a valueproportional to only the voltage Vcc because of no laser oscillation.

Then the voltage VA is compared with 90% of the reference voltage Vrefby means of the comparator 45. As a result, since the voltage VA islower than the reference voltage Vref, the comparator 45 outputs an high(H) level signal, as shown as the voltage VA between the time a and thetime b as well as the output (1) of the comparator 45.

When the analog switch 39 receives an H level signal and turns on, theresistor 40 is connected in parallel to the resistor 41, the voltage VAis applied to the operational amplifier 36 and the capacitor 35 via theresistors.

As a result, since the time constant that the output voltage VB of theoperational amplifier 36 increases or decreases is Tc mV/sec, theoperational amplifier 36 increases its output voltage VB from thereference voltage Vref in accordance with the time constant Tc mV/sec.Thus the base current IB of the transistor 31 increases with the timeconstant Tc mV/sec while the collector current thereof as an LD drivecurrent lop is increased.

In the above manner, a current which increases at a predeterminedcurrent varying rate can be supplied to the laser diode 11. However,since the voltage VB does not exceed the threshold voltage α (refer to αin FIG. 10) prior to the time b, the laser diode 11 does not perform anylaser oscillation.

As shown with the time b in FIG. 10, when the output voltage VB of theoperational amplifier 36 exceeds the threshold voltage α of the laserdiode 11, or the monitoring voltage VA exceeds the voltage at the timeb, the laser diode 11 starts its laser oscillation. Then till thevoltage VA equalizes with the reference voltage Vref, the operationalamplifier 36 increases its output voltage VB based on the time constantTc mV/sec.

Sequentially, the following process will be made between the time b andthe time c. With the laser oscillation of the laser diode 11, thecurrent Im from the external photo diode 12 increases proportionally tothe voltage Vcc and the light amount.

The voltage converted from the current Im by the variable resistor 37and the operational amplifier 38 is divided to a voltage VAcorresponding to the light amount to apply it to the negative input sideof the amplifier 36 and the comparator 45. Naturally the voltage VAincreases proportionally to the current Im.

However, since the voltage VA is lower than 90% of the reference voltageVref between the time b and the time c, the resistor 40 is keptconnected. As a result, in the span, the output VB of the operationalamplifier 36 increases sequentially with the time constant of Tc mV/secso that the laser output of the laser diode 11 increases with the LDdrive current Iop in accordance with the time constant Tc mV/sec.

As indicates with the time c, when the voltage VA is equalized with the90% of the reference voltage Vref, the comparator 45 produces an low (L)level signal to turn off the analog switch 39.

Since the resistor 40 is disconnected after the time c, the timeconstant is changed from the Tc mV/sec to Tc/100 mV/sec, the outputvoltage VB of the operational amplifier 36 varies with the timeconstant. At this time, the voltage VB is dropped to a value quite lowerthan the value that the laser diode 11 emits at a predetermined lightamount p.

When the output voltage VB of the operational amplifier 36 rises inaccordance with the time constant of Tc/100 mV/sec, the voltages VA andVref applied respectively to the positive input side and the negativeinput side of the operational amplifier 36 are equalized to each other(refer to the time d in FIG. 10), whereby the output voltage VB of theoperational amplifier 36 is maintained at a fixed value to emit apredetermined light amount p.

When the output voltage reaches the predetermined value, the operationalamplifier 36 compensates with the time constant Tc/100 mV/sec so as tomaintain the predetermined value with respect to the laser outputvariations due to various causes. Thus a laser output compensation canbe performed at a moderate varying rate, instead of the higher ratecompensation at the time constant of Tc mV/sec.

As a result, since the signal current sent to the base of the transistor31 is at a fixed value, the LD drive current Iop is maintained to emitthe light amount p. When the laser diode 11 is emitting in apredetermined light amount p with the reference voltage Vref, even ifnoise is induced in the feedback system due to a certain cause, the timeconstant is changed to a small value of the Tc/100 mV/sec near to thepredetermined value producing the predetermined light amount p. Thus theoutput of the operational amplifier 36 does not fall sharply so that anabnormal light emission of the laser diode 11 can be prevented.

Since the time constant is Tc mV/sec while the predetermined lightamount p is obtained, the output of the operational amplifier 36 canrise near to the predetermined light amount generating amount at amoderate rate. When the analog switch 34 is turned on in response to thecontrol signal from the CPU, the operational amplifier 36 outputs thereference voltage Vref so that the transistor 31 is turned off to cutoff the laser.

According to the first embodiment of the present invention, when thelight amount of the laser diode 11 is less than a predetermined value,the first feedback control means with the resistor 40 selects thecontrol mode, thus executing a feedback control of the light amount ofthe semiconductor laser with the first time constant. When the lightamount of the laser diode 11 is more than a predetermined value, thesecond feedback control means without the resistor 40 selects thecontrol mode, thus executing a feedback control of the light amount ofthe semiconductor laser 11 with the second time constant longer than thefirst time constant. Hence a feedback control can be performed inaccordance with the light emitting amount of the laser diode 11. Such aneffect can be established by adding a small device to the semiconductorlaser control device, thus reducing the manufacturing cost.

(c) Explanation of the Second Embodiment

FIG. 11 is a diagram showing the second embodiment of the presentinvention. In FIG. 11, numeral 20B represents a semiconductor lasercontrol device. The semiconductor laser control device 20B can bearranged in place of the laser control devices 3 and 3A. Thesemiconductor laser control device 20B is constituted of an LD chip 30including a laser diode 11 and a photo diode 12 arranged in parallel toeach other, a transistor 31, analog switches 34 and 39, amplifiers 36and 38, a reference voltage source 42, a capacitor 35, a variableresistor 37, resistors 32, 33, 40 and 41, and a timer 50.

In the devices, like numerals represent like elements in thesemiconductor laser control device 20A in the first embodiment. Thesemiconductor laser control device 20B includes a timer 50 and an analogswitch 34 which receive a control signal from a CPU, and an analogswitch 39 connected to the CPU, instead of the comparator 45 as acontrol mode selecting means and the resistors 43 and 44.

When the CPU inputs an on/off control signal of an L level to the analogswitch 34, the timer 50 activates and outputs an L level signal after apredetermined period of time c. The timer 50 receives an L level signalfrom the CPU and outputs an L level signal after the predetermined timec.

The predetermined time c, as shown in FIG. 10, is set so as to be longerthan the time when the laser diode 11 produces a predetermined lightamount of with the time constant of 1 mV/sec when the resistor 40 isadded.

In such a structure, when the CPU sends an L level signal to the analogswitch 34 and the timer 50, the semiconductor laser control device 20Bactivates while the timer 50 starts to count the predetermined time c.

As shown in FIG. 10, when the voltage VB applied the base of thetransistor 31 exceeds the threshold voltage α, the LD drive current Iopsent to the semiconductor laser 11 emits the semiconductor laser 11.

While the timer 50 makes the analog switch 39 on for a predeterminedperiod c of time, the resistor 40 is connected in parallel to theresistor 41.

During the period, when the control mode of the time constant of TcmV/sec is selected, the output voltage VB of the operational amplifier36 rises with the time constant (refer to the starting time a to thetime c seen in FIG. 10). The feedback control of the light amount of thelaser diode 11 is performed in accordance with the time constant of TcmV/sec.

When the light amount is over the predetermined value α at thepredetermined time c, the timer 50 outputs an L level signal to turn offthe analog switch 39 so that the resistor 40 is disconnected from theresistor 41 connected in parallel thereto.

As a result, the control mode of the time constant of Tc/100 mV/sec isselected, the output voltage VB of the operational amplifier 36 riseswith the time constant. The feedback control of the light amount of thelaser diode 11 is performed in accordance with the time constant Tc/100mV/sec (refer to the area after the time c seen in FIG. 10).

Then the operational amplifier 36 increases its output voltage VB atslow rate in accordance with the time constant of Tc/100 mV/sec. Whenthe laser diode 11 reaches the predetermined light amount p, the voltageat that time is maintained. Various processes follow in the similarmanner to the first embodiment.

When the analog switch 34 is turned on in accordance with the controlsignal from the CPU, the output signal of the operational amplifier 36becomes the reference voltage Vref so that the transistor 31 is turnedoff to cut the laser light.

According to the second embodiment, the first time constant is switchedto the second time constant at a predetermined time c longer than thepredetermined light amount reaching time of the semiconductor laser 11based on the first time constant Tc mV/sec. Hence the similar effect tothat of the semiconductor laser control device 20A in the firstembodiment can be obtained by a simplified structure where a smalldevice is added merely to the semiconductor laser control device. Thisstructure can reduce the manufacturing cost.

(d) Explanation of the Third Embodiment

FIG. 12 is a block diagram showing the third embodiment of the presentinvention. In FIG. 12, numeral 20C represents a semiconductor lasercontrol device. The semiconductor laser control device 20C is arrangedin place of the semiconductor laser control devices 3 and 3A. Thesemiconductor laser control device 20C is constituted of an LD chip 30including a laser diode 11 and a photo diode 12 arranged in parallel, atransistor 31, analog switches 34 and 39, amplifiers 36 and 38,reference voltage sources 42 and 52, a capacitor 35, variable resistors37 and 53, resistors 32, 33, 51, 54 and 55, and a comparator 45.

In those devices, like numerals represent elements forming thesemiconductor laser control devices 20A and 20B in the first and secondembodiments. The semiconductor laser control device 20C includes as acontrol mode selecting means a reference voltage source 52, a variableresistor 53, a comparator 45, and a resistor 51, instead of the timer 50of the semiconductor laser control device 20B in the second embodiment.The resistors 54 and 55 are arranged in place of the resistors 40 and41.

The comparator 45 has a positive input side receiving a voltage dividedfrom the reference voltage Vref from the reference voltage source 52 bythe variable resistor 53, and a negative input side receiving theemitter output of the transistor 31. The comparator 45 also has anoutput side connected to the analog switch 39. With the use of thereference voltage source 52, the variable resistor 53, and the resistor51, the comparator 45 compares the voltage on the positive input withthe voltage on the negative input. When the emitter output reaches alevel which emits the collector output for producing a predeterminedlight amount r, the comparator 45 outputs an L level signal.

The predetermined light amount r is set to be slightly a lower valuethan the predetermined light amount p. In other words, the value(predetermined LD drive current value Iopr) at which the collectorcurrent (LD drive current Iop) produces the predetermined light amount rto the laser diode 11 is set to be a lower value slightly than thecurrent value (predetermined LD drive current value Iopp) for producinga predetermined light amount p.

In the device 20C, the resistors 54 and 55 arranged in place of theresistors 40 and 41 are used to set the time constants of the outputs ofthe operational amplifier 36 to, for example, 10 Tc mV/sec or Tc/100mV/sec. That is, when the resistor 54 is connected in parallel to theresistor 55, the time constant is 10 TcmV/sec. When the resistor 54 isdisconnected from the resistor 55, the time constant is Tc/100 mV/sec.

In the semiconductor laser control device 20C, when the LD drive currentIop of the laser diode 11 is less than the predetermined drive current,the feedback of the light amount of the laser diode 11 is performedbased on the first time constant of 10 Tc mV/sec. When the LD drivecurrent Iop is more than the predetermined drive current, the feedbackof the light amount of the laser diode 11 is performed based on thesecond time constant Tc100 mV/sec.

In the above structure, as shown with (1) and (2) in FIG. 13, when theanalog switch 34 is turned off in response to the control signal in theCPU, the current Im indicating a detected laser light amount isconverted to a voltage and divided to the voltage VA corresponding tothe light amount by means of the variable resistor 37.

Since the voltage VB applied to the base of the transistor 31 does notreach the emitter current value producing a predetermined light amount rprior to the time f, the comparator 45 outputs an H level signal. Thusthe resistor 40 is connected to the resistor 41 in parallel. The outputvoltage VB of the operational amplifier 36 rises with the time constantof 10 Tc mV/sec by the time f.

With the increase in the base voltage VB of the transistor 31, when thetime f has come, the emitter current and the collector current reachrespectively a value producing the predetermined light amount r.

As a result, the comparator 45 outputs an L level signal to the analogswitch 39 to disconnect the resistor 40 from the resistor 41. After thetime f, the output voltage VB of the operational amplifier 36 rises withthe time constant of Tc/100 mV/sec.

When the output voltage VB of the operational amplifier 36 exceeds thethreshold voltage α of the laser diode 11 at the time b, the laser diode11 starts its laser oscillation.

Then the operational amplifier 36 increases slowly the voltage VB inaccordance with the time constant Tc/100 mV/sec. The operationalamplifier 36 maintains the voltage when the light amount of the laserdiode 11 reaches at a predetermined value p at the time e. Variousprocesses follows sequentially in the similar manner to the firstembodiment.

When the analog switch 34 is turned on in accordance with the controlsignal from the CPU, the output of the operational amplifier 36 becomesthe reference voltage Vref so that the transistor 31 is turned off tocut the laser emission.

As described above, when the drive current of the laser diode 11 reachesa predetermined value, the first time constant of 10 TcmV/sec isswitched to the second time constant of Tc/100 mV/sec. Thus arrangingmerely a small device to the laser control device causes the similareffect to that in the semiconductor laser control device 20A in thefirst embodiment.

Moreover, since the LD drive current Iop of the semiconductor laser 11is directly measured, if an abnormal state occurs in the main feedbacksystem, the time constant can be switched at an exact timing operation.

Moreover after the power source is switched on, the LD drive current Iopcan be increased swiftly near to the value producing a predeterminedlight amount p in accordance with a curve of the second ordercharacteristic.

(e) Explanation of the Fourth Embodiment

FIG. 14 is a block diagram showing the fourth embodiment of the presentinvention. In FIG. 14, numeral 20D represents a semiconductor lasercontrol device. The semiconductor laser control device 20D is arrangedin place of the semiconductor laser control devices 3 and 3A. Thesemiconductor laser control device 20D is constituted of an LD chip 30including a laser diode 11 and a photo diode 12 arranged in parallel toeach other, a transistor 31, analog switches 34, 39 and 48, amplifiers36 and 38, reference voltage sources 42, and 52, a capacitor 35,variable resistors 37 and 53, resistors 32, 33, 41, 43, 44, 47, 51, 54and 55, and comparators 45 and 46D.

In the semiconductor laser control devices 20A, 20B and 20C according tothe first, second, and third embodiments, like numerals represent likeelements. The semiconductor laser control device 20D includesadditionally the reference voltage source 52, the variable resistor 53,the comparator 45, and the resistor 51 which act as the control modeselecting means in the semiconductor laser control device 20C of thethird embodiment in the semiconductor laser control device 20C, to thesemiconductor laser control device 20A of the first embodiment.

In the previous embodiments, the resistor 47 is connected in parallel tothe resistors 40 and 41 and the analog switch 34 functioning as thefirst and second feedback control means. The resistor 47 is connectedserially to the switch 48. The switch 48 is connected so as to becontrolled on/off in response to the output from the comparator 46D.

The resistor 47 has the same value as that of the resistor 41. Theanalog switch 48 is made of the same types as the analog switches 34 and39, and the comparator 46D is the same type as the comparator 45.

The resistors 40, 41, and 47 are used to adjust the time constant of theoutput of the operational amplifier 36 in the device 20D to 10 Tc mV/sec(first time constant), Tc mV/sec (second time constant), or Tc/100mV/sec (third time constant). When the resistors 40 and 47 are connectedin parallel to the resistor 41, they act as the first feedback controlmeans with the time constant of 10 TcmV/sec. When the resistor 47 isdisconnected from the analog switch 48 and the resistor 40 is connectedin parallel to the resistor 41, they act as the second feedback controlmeans with time constant of Tc mV/see. When the analog switches 39 and48 disconnect respectively the resistors 40 and 47 from the resistor 41,the structure functions as the third feedback control means with thetime constant of Tc/100 mV/sec. As described above, the third timeconstant is set to be longer than the second time constant. The secondtime constant is so as to be longer than the first time constant.

The comparators 45 and 46D for selecting the resistors 40, 41 and 47,and various devices act as drive current measuring means and controlmode selecting means. That is, when the LD drive current Iopr is lessthan a predetermined value based on the LD drive current Iop and thedrive current measuring result, the first feedback means selects acontrol mode. When the LD drive current Iopr is more than thepredetermined value, the second feedback control means selects thecontrol mode. When the light amount of the laser diode 11 is larger thanthe predetermined light amount q, the third feedback control meansselects the control mode.

As described in the third embodiment, the collector current(predetermined LD drive current value Iopr) of the transistor 31producing a predetermined light amount r is set to a lower valueslightly than the collector current (predetermined LD drive currentvalue Iopr) producing a predetermined light amount p.

In the above structure, as shown with (1) and (2) in FIG. 15, the analogswitch 34 is turned off in response to the control signal from the CPU,the current Im indicating the detected laser light amount is convertedto a voltage and divided to a voltage VA corresponding to the lightamount by means of the variable resistor 37.

When the LD drive current Iop of the semiconductor laser 11 whichproduces in accordance with the base voltage VB of the transistor 31till the time f is less than a predetermined value, and is less than apredetermined value, the first feedback control means selects thecontrol mode. That is, since the feedback control of the light amount ofthe laser diode 11 is performed based on the first time constant of 10Tc mV/sec, the output voltage VB of the operational amplifier 36 risesaccording to the first time constant.

With the increase of the voltage VB at the time f, the LD drive currentIop through the emitter reaches at a predetermined drive current valueIopr. Then since the comparator 46D outputs the L level signal to theanalog switch 48, the resistor 47 connected in parallel to the resistors40 and 41 is disconnected. Thus the second feedback control meansselects the control mode so that the voltage VB rises in accordance withthe time constant Tc mV/sec.

Then when the output voltage VB of the operational amplifier 36 exceedsthe threshold value α of the laser diode 11 at the time b, the laserdiode 11 oscillates.

At the time c, since the base voltage of the transistor 31 rises withthe voltage VB, the collector current and the emitter current reachrespectively at a predetermined value producing a predetermined lightamount q.

As a result, the voltage VA on the negative input of the comparator 45is equalized with 90% of the reference voltage Vref so that thecomparator 45 outputs an L level signal to the analog switch 39.

Thus when the resistor 40 connected in parallel to the resistor 41 isdisconnected, the output voltage of the operational amplifier 36 risesin accordance with the third time constant Tc/100 mV/sec after the timec. In other words, when light amount q exceeds the predetermined value,the third feedback control means selects the control mode.

Then the operational amplifier 36 raises slowly its output voltage VBbased on the time constant of Tc/100 mV/sec. When the laser diode 11emits at the predetermined light amount p at the time g, the voltage ismaintained. Various processes follow sequentially in the similar mannerto that of the first embodiment.

When the analog switch 34 is turned on in response to the control signalfrom the CPU, the output of the operational amplifier 36 becomes thereference voltage Vref, thus turning off the transistor 31 to glow offthe laser. FIG. 15 does not show the voltage VB because it resemblesnearly the voltage VA.

As described above, when the drive current of the laser diode 11 reachesa predetermined value Iopr, the control mode is switched from the firsttime constant of 10 Tc mV/sec to the second time constant of Tc mV/sec.Furthermore, when the light amount reaches a predetermined value q, thecontrol mode is switched from the second time constant of Tc mV/sec tothe third time constant of Tc/100 mV/sec. Hence the similar effect tothat of the semiconductor laser control device 20A according to thefirst and third embodiments can be established by adding merely a smalldevice to the semiconductor laser control device. In comparison with thethird embodiment, the LD drive current Iop can be increased near to avalue producing the light amount p at earlier rate after the powersource is switched on.

(f) Explanation of the Fifth Embodiment

FIG. 16 is a block diagram showing the fifth embodiment according to thepresent invention. In FIG. 16, numeral 20E represents a semiconductorlaser control device. The semiconductor laser control device 20E isarranged in place of the semiconductor laser control devices 3 and 3A.The semiconductor laser control device 20E is constituted of an LD chip30 including a laser diode 11 and a photo diode 12 arranged in parallelto each other, a transistor 31, analog switches 34 and 58, amplifiers 36and 38, reference voltage power source 42, capacitors 35 and 49, acomparator 45, a variable resistor 37, and resistors 32, 33, 41, 54, 55,56, and 57.

In the above devices, like numerals represent like elements in thesemiconductor laser control devices 20A, 20B, 20C, and 20D of the first,second, third, and fourth embodiments. The semiconductor laser controldevice 20E includes an analog switch 58, resistors 54 and 55, and acapacitor 49, instead of the resistor 40 and the analog switch 39 in thesemiconductor laser control device 20A in the first embodiment.

The resistor 54 has an current input side connected to the externalphoto diode 12 via the analog switch 58, and an output side connected tothe variable resistor 37 and the capacitor 49. The resistor 55 isconnected in parallel to a serial circuit of the analog switch 58 andthe resistor 54, and also is connected to the capacitor 49.

The above circuit structure acts as a low pass filter which passes thelow frequency component in the monitoring current Im from the externalphoto diode 12. When the analog switch 58 is turned on in response tothe L level signal, the above structure is connected as a low passfilter to the feedback system (feedback control means) to input themonitoring signal (voltage VA) from the external photo diode 12. Thusthe operational amplifier 36 is controlled so as to moderate its outputvoltage variation.

The comparator 45 acts as a selecting means. When the light amount ofthe laser diode 11 obtained based on the monitoring result from theexternal photo diode 12 exceeds the predetermined value s, thecomparator 45 outputs an L level signal. The predetermined light amounts is somehow lower than the predetermined light amount p.

In such a structure, as shown with (1) in FIG. 16, when the analogswitch 34 is turned off in response to the control signal from the CPU,the current Im indicating the laser light amount detected is convertedto a voltage and divided to a voltage VA corresponding to the lightamount. In this case, the analog switch 58 is in off state, thus passingno current Im through the resistor 54.

The reason is that the light amount of the laser diode 11 is not at thepredetermined value s immediately after the power source is switched onwhile the comparator 45 outputs an H level signal because the current Imis less than the predetermined light amount s corresponding to 90% ofthe reference voltage Vref.

That is, the light amount of the laser diode 11 is subjected to afeedback control with the shorter time constant till the light amountreaches the predetermined value s so that the output voltage VB of theoperational amplifier 36 rises in accordance with the time constant.

When the light amount reaches the predetermined value s, the current Imexceeds a value corresponding to the 95% of the reference voltage Vrefcorresponding to the predetermined light amount s so that the comparator45 outputs an L level signal.

Then the analog switch 58 is turned on and the current Im flows throughthe resistor 54 connected in parallel to the resistor 55. As a result, alow pass filter is formed together with the capacitor 49 and delays thefeedback system by transmitting the low frequency component of thecurrent Im to the feedback system.

In order to control the light amount of the laser diode 11, the outputvoltage VB of the operational amplifier 36 is subjected to a feedbackcontrol from a slight smaller value of the predetermined light amount p,based on the time constant longer than the above time constant.Sequentially various processes follow in the similar manner to that inthe first embodiment.

When the analog switch 34 turned on in response to the control signalfrom the CPU, the output voltage of an operational amplifier 36 becomesthe reference voltage Vref while the transistor 31 is turned off to cutthe laser emission.

The similar effect to that in the semiconductor laser diode 20Aaccording to the first embodiment can be obtained by connecting ordisconnecting the low pass filter based on the predetermined lightamount s as a threshold value. Unlike the first embodiment, the feedbacksystem has a time constant varying component arranged to the input sideof the operational amplifier 38. Hence the flexibility in the design ofthe semiconductor laser control device is widen like the firstembodiment.

(g) Explanation of the Sixth Embodiment

FIG. 17 is a block diagram showing the sixth embodiment according to thepresent invention. In FIG. 17, numeral 20F represents a semiconductorlaser control device. The semiconductor laser control device 20F isarranged in place of the semiconductor laser control devices 3 and 3A.The semiconductor laser control device 20F includes a timer 50 arrangedbetween the output of the comparator 45 and the analog switch 58 in thesemiconductor laser control device 20E of the fifth embodiment.

The timer 50 is similar to that of the second embodiment. Particularly,in this case, the timer 50 activates when the received signal is an Llevel signal. When a period u of time previously registered andpredetermined has passed, the timer itself produces an L level signal.

The total period obtained by adding the predetermined period u to theperiod between the time that the analog switch 34 has been turned offand the time that the light amount s is established is set so as to beshorter slightly than the period between the time that the analog switch34 has been turned off and the time that the laser diode 11 emits at thepredetermined light amount p.

The comparator 45 inputs the monitoring signal from the external photodiode 12 to the feedback system through the low pass filter based on themonitoring result (current Im) from the external photo diode 12 andafter a lapse of the predetermined time u from the time that the lightamount is more than the predetermined value s.

In the above structure, the comparator 45 controls a feedback of thelight amount of the laser diode 11 with a shorter time constant based onthe monitoring result from the external photo diode 12 and within thepredetermined time u after the light amount has been more than thepredetermined value s.

When the predetermined time u passes after the light amount of the laserdiode 11 has exceeded the predetermined value s, the comparator 45distributes the current Im to the low pass filter forming elements.

The low frequency component of the current Im is sent to delay thefeedback system. As a result, the output voltage VB of the operationalamplifier 36 controls the light amount of the laser diode 11 with a timeconstant longer than the previous time constant and from the valuesmaller than the predetermined light amount p. The time constantswitching timing can change arbitrarily by varying the predeterminedtime u registered by the timer 50. Since the switching timing isconsidered in the time reaching the predetermined light amount s, thetimer 50 can control with no time deviation to the predetermined timeand high reliability. Sequentially, various processes follow in thesimilar manner to that in the first embodiment.

(h) Explanation of the Seventh Embodiment

FIG. 18 is a block diagram showing the seventh embodiment according tothe present invention. In FIG. 18, numeral 20G represents asemiconductor laser control device. The semiconductor laser controldevice 20G is arranged in place of the semiconductor laser controldevices 3 and 3A. The semiconductor laser control device 20G isconstituted of an LD chip 30 including a laser diode 11 and a photodiode 12 arranged in parallel to each other, a transistor 31, analogswitches 34 and 58, amplifiers 36 and 38, a reference potential source42, capacitors 35 and 49, a variable resistor 37, a timer 50, andresistors 32, 33, 41, 54, and 55.

In the above devices, like numerals represent like elements forming thesemiconductor laser control devices 20A, 20B, 20C, and 20D of the first,second, third, fourth, fifth, and sixth embodiments. That is, thesemiconductor laser control device 20G includes a timer 50 for receivingthe output of the CPU, in place of the resistors 56 and 57 and thecomparator 45 in the fifth embodiment of the present invention. Theoutput of the timer 50 is connected so as to control the analog switch58.

The timer 50 is one similar to that used in the previous embodiment.Particularly, in this case, when the preregistered and predeterminedperiod v of time has passed, the timer 50 is set to output an L levelsignal.

The predetermined period v is set so as to be shorter slightly than theperiod of time taken from the time that the analog switch 34 is turnedoff to the time that the laser diode 11 emits at the predetermined lightamount p.

Like the semiconductor laser control device 20E in the fifth embodiment,when the analog switch 58 is turned on in response to the L level signalfrom the timer 50, it inputs the monitoring signal (current Im) from theexternal photo diode 12 to the feedback system via the low pass filter.

In the above structure, when the predetermined period v is passed afterthe laser diode 11 has been changed from an off state to an on state,the current Im is inputted to the feedback system via the low passfilter forming elements by means of the timer 50 and the analog switch58.

As a result, the time constant is changed, for example, from TcmV/sec toTc/100 mV/sec at a value near to the predetermined light amount p sothat the output voltage of the operational amplifier 36 is subjected toa proper feedback control near to or at the predetermined light amountp.

Even a small circuit structure can vary arbitrarily the time constantswitching timing by varying the predetermined time v registered in thetimer 50. Sequentially various operations follow further in the similarmanner to that in the first embodiment.

(i) Explanation of the Eighth Embodiment

FIG. 19 is a block diagram showing the eighth embodiment according tothe present invention. In FIG. 19, numeral 20 represents a semiconductorlaser control device. The semiconductor laser control device 20 isarranged in place of the semiconductor laser control devices 3 and 3A.The semiconductor laser control device 20 also includes an LD chip 30including a laser diode 11 and a photo diode 12 arranged in parallel toeach other, a transistor 31, an analog switch 34, a capacitor 35,amplifiers 36 and 38, a reference voltage source 42, resistors 32, 33and 46, resistors 61, 62, and 63 acting as a current/voltage converter,an analog switch 24 acting as a monitoring voltage dividing means, aresistor 59, and a variable resistor 25. The operational amplifier 36acts as feedback control means.

In the above devices, like numerals represent like elements in thesemiconductor laser control device in each embodiment. That is, in thesemiconductor laser control device 20, the resistor 59 is arrangedbetween the operational amplifier 38 and the variable resistor 25 in thesemiconductor laser control device 3A described above. The analog switch24 is connected in parallel to the resistor 59.

As described with the device shown in FIG. 26, the circuit configurationof the resistors 61, 62, and 63 converts the current Im flowing thepositive and the negative inputs sides of the operational amplifier 38to a voltage divided in a predetermined ratio.

Since the operational amplifier 36 has the negative input side connectedto no time constant varying resistor, it integrates the output voltagewith the time constant determined by the resistor 46 and maintains it ata predetermined value.

The analog switch 24 is turned on or off in accordance with an externalcontrol and short-circuits the resistor 59 connected in parallelthereto. The resistor 59 drops the voltage Vm from the operationalamplifier 38 in a predetermined ratio when the analog switch 24 isturned off. The resistance value of the resistor 59 is set not to emitexcessively the light emitting diode 11 without depending the on/offstate of the analog switch 24 when the variable resistor 25 is adjustedto its minimum resistance value and the current Im at the minimum valueflows. The variable resistor 25, as described with the device in FIG.26, varies continuously the voltage dividing ratio.

The above structure, as shown in FIG. 19, executes in the similar mannerto that in the prior art. That is, the external photo diode 12 detectsthe current Im indicating the laser light amount. As shown in FIG. 25,the operational amplifier 36 equalizes the voltage VA corresponding tothe current Im with the reference voltage Vref and subjects the LD drivecurrent Iop of the semiconductor laser 11 to a feedback control tomaintain the laser light amount at a fixed value.

The laser diode 11 and the external photo diode 12 on the LD chip 30 maybe of the same type in the mounting condition. In this case, the currentIm to the light amount of the laser diode 11 may vary but the voltage tothe negative input side of the operational amplifier 36 can becompensated to a proper value by dividing the voltage by the variableresistor 25.

Then when the analog switch 24 is turned on, the voltage Vm from theoperational amplifier 38 is directly supplied to the variable resistor25, as shown with the voltage division ratio K on the left side in FIG.20. Therefore the range of the voltage division ratio K to the currentIm is similar to that of the related art shown in FIG. 27.

As shown with the voltage division ratio K on the right side in FIG. 20,when the analog switch 24 is turned off, the voltage Vm from theoperational amplifier 38 is supplied to the resistor 25 via the resistor54. Hence the range of the voltage division ratio K to the current Im iswidened in accordance with the resistance value of the resistor 59. Inother words, since the resistor 59 can drop previously the voltagedivided by the variable resistor 25, the voltage division ratio K to therotational angle of the resistance adjusting knob can be widened.

In the similar manner to that of the prior art, each value in the figurehas the relations including current Im=light amount P0×light amount P5/5mW, voltage Vm=current Im×resistance value of resistance 61, andK=reference voltage Vref/voltage Vm.

As a result, as shown by the light amount of 2 mW to 4 mW in the figure,since the range of the voltage division ratio K to the current Im can bewidened, the current can be adjusted without using a special device evenif the current Im becomes large. Such an effect can be obtained byadding merely a small device to the semiconductor laser control device,thus being superior in a manufacturing cost.

A variable resistor may be used instead of the resistor 59. In thiscase, the voltage division ratio K can be adjusted continuously andpurposely. The maximum resistance value of the resistor is set so as notto emit excessively the laser diode 11 even if the analog switch 24 isturned on or off when the resistor 25 is adjusted to its minimumresistance value and the current Im is at a minimum value.

(j) Explanation of the Ninth Embodiment

FIG. 21 is a cross sectional view showing an LD chip mounted on a heatsink according to the ninth embodiment of the present invention. FIG. 22is a diagram viewed from the terminal side of the LD chip removed fromthe printed board 74. In FIGS. 21 and 22, the LD chip 30 is used in thesemiconductor laser control device, as described in the foregoingembodiments.

The LD chip 30 is contained in the container 70 formed of the case 71and the heat sink (heat dissipating member) 28. The LD chip 30 iscontacted with the heat sink 28 via the plastic intermediate member 27.The heat sink 28 is formed of a member 78 conducting heat generated inthe LD chip 30, and a heat dissipating surface 79 for dissipating heatsent from the heat conducting member 78. The heat conducting member 78and the heat dissipating member 79 are made of a non-conductive materialof a high transfer rate such as aluminum. The plastic member 27 is madeof a non-conductive material having a thickness equivalent to thethermally contacted member.

The LD chip 30, as shown in FIG. 9, includes a laser diode 11 and anexternal photo diode 12 and has three pins for connecting electricallyto the devices.

The LD chip 30 is fixed by inserting the three pins in the printed board72 through corresponding three holes of cover member 73. The printedboard 74 is fixed to the case 71 together with the heat sink 28 withfour screws 75 in the recesses 77. The three terminals of the LD chip 30are inserted to the cover member 73 through the corresponding holes 76.The screws 75 are made of an electrical conducting material such asmetal. The screws 75 penetrate the heat conducting member 78 of the heatsink 28 so as to contact electrically with the case 71. One of thescrews 75 is connected to the ground line 80. The recesses 77 are formedthrough the printed board 74, the heat conducting portion 78 of the heatsink 28, and the case 71. In FIG. 22, the chain line shows an exampleincluding a printed board 74 and a pattern printed thereon.

According to the above structure, heat generated in the LD chip 30 isconducted to the conducting member 78 of the heat sink 28 via theplastic member 27 to dissipate externally from the heat dissipatingsurface 79. As a result, the laser diode 11 and the external photo diode12 in the LD chip 30 can be prolonged in the operational life.

If the heat dissipating surface 79 receives external electromagneticwaves and electrostatic noises on the effect of an antenna, the noisesare not transmitted to the LD chip 30 because the plastic intermediatemember 27 shields them. As a result, the heat sink 28 is held at a fixedpotential different from that of the LD chip 30.

The current generated in the heat sink 28 due to noises flows from thescrew 75 contacted to the ground line 80 through the conduction member78 of the heat sink 28. Thus an undesired current flowing to the laserdiode 11 and the external photo diode 12 in the LD chip 30 are preventedand the diodes can be prolonged in its operational life. As a result,the laser diode 11 and the external photo diode 12 has a strong immunityto noises so that the semiconductor laser control device can improve itsstability and accuracy. The replacement of the diode is not nearlyneeded and accordingly the device becomes very economical. The similareffect can be obtained by using an intermediate member such as glass orsilicon, in place of the plastic intermediate member 27.

What is claimed is:
 1. A semiconductor laser control method wherein alight amount generated by a semiconductor laser, permitting a lightamount control in accordance with current, is subjected to a feedbackcontrol based on a predetermined time constant while the light amount ofsaid semiconductor laser is monitored, comprising the steps of:inputtinga light amount monitoring signal to a feedback control means withoutpassing through a low pass filter till the light amount of saidsemiconductor laser reaches a first light amount not being zero; andinputting said light amount monitoring signal to said feedback controlmeans via said low pass filter when a light amount of said semiconductorlaser is larger than said first light amount.
 2. A semiconductor lasercontrol device comprising:a semiconductor laser permitting a lightamount control in accordance with current; light amount monitoring meansfor monitoring a light amount of said semiconductor laser; feedbackcontrol means for controlling a feedback of said light amount of saidsemiconductor laser with a predetermined time constant based on amonitoring result from said light amount monitoring means; low passfilter for passing a low frequency component of a monitoring signal fromsaid light amount monitoring means; and selecting means for inputting alight amount monitoring signal to a feedback control means withoutpassing through a low pass filter till the light amount of saidsemiconductor laser reaches a first light amount not being zero, basedon said monitoring result from said light amount monitoring means, andinputting said monitoring signal from said light amount monitoring meansto said feedback control means through said low pass filter when thelight amount of said semiconductor laser is larger than said first lightamount.
 3. A semiconductor laser control method wherein a light amountgenerated by a semiconductor laser, permitting a light amount control inaccordance with current, is subjected to a feedback control based on apredetermined time constant while the light amount of said semiconductorlaser is monitored, comprising:a first step of inputting a light amountmonitoring signal to said feedback control means via a low pass filterafter a first period of time not being zero when a light amount of saidsemiconductor laser is larger than a second light amount not being zero;and a second step of inputting said light amount monitoring signal tosaid feedback control means via no low pass filter, during time periodother than said first inputting step.
 4. A semiconductor laser controldevice comprising:a semiconductor laser permitting a light amountcontrol in accordance with current; light amount monitoring means formonitoring a light amount of said semiconductor laser; feedback controlmeans for controlling a feedback of said light amount of saidsemiconductor laser with a predetermined light amount based on amonitoring result from said light amount monitoring means; low passfilter for passing a low frequency component of a monitoring result fromsaid light amount monitoring means; and selecting means for firstinputting said monitoring signal from said light amount monitoring meansto said feedback control means through said low pass filter after afirst period of time not being zero when a light amount is larger than asecond light amount not being zero based on said monitoring result fromsaid light amount monitoring means and for second inputting said lightamount monitoring signal to said feedback control means via no low passfilter during time period other than said first inputting operation. 5.A semiconductor laser control method wherein a light amount generated bya semiconductor laser, permitting a light amount control in accordancewith current, is subjected to a feedback control based on apredetermined time constant while the light amount of said semiconductorlaser is monitored, comprising:a first step of inputting a light amountmonitoring signal to said feedback control means via a low pass filterafter a second period of time not being zero when said semiconductorlaser has been changed from an off state to an on state; and a secondstep of inputting said light amount monitoring signal to said feedbackcontrol means via no low pass filter, during time period other than saidfirst inputting step.
 6. A semiconductor laser control devicecomprising:a semiconductor laser permitting a light amount control inaccordance with current; light amount monitoring means for monitoring alight amount of said semiconductor laser; feedback control means forcontrolling a feedback of said light amount of said semiconductor laserwith a predetermined light amount based on a monitoring result from saidlight amount monitoring means; low pass filter for passing a lowfrequency component of a monitoring result from said light amountmonitoring means; on/off control means for controlling the on/offoperation of said semiconductor laser; and selecting means for firstinputting a monitoring signal from said light amount monitoring means tosaid feedback control means via said low pass filter after a secondperiod of time not being zero when semiconductor laser has been changedfrom an off state to an on state by said on/off control means and forsecond inputting said light amount monitoring signal to said feedbackcontrol means via no low pass filter, during time period other than saidfirst inputting operation.